LONDON — Documents published by the Guardian newspaper are providing new insight into the National Security Agency's surveillance of world data, giving an over-the-shoulder look at the programs and techniques U.S. intelligence analysts use to exploit the hundreds of billions of records they gather each year.

Dozens of training slides published Wednesday divulge details about XKeyscore, one of a family of NSA programs that leaker Edward Snowden says has given America the ability to spy on "the vast majority of human communications."